Do you have all the mdia that is in the project too? If not, even if you manage to get it open, all the media will be listed as 'offline'.
If you do have the media (all the stuff you captured that is used in the project) on an external drive or something and you think you can get it to reconnect properly, try adding the suffix .fcp to the end of your project name. This might help, but it could also be that your project file should have been zipped before emailing, because sometimes parts of the file get mucked up during email processes.
Also, if you do have the media on an external drive, next time add the project file to the external too. It's bound to be less than 100MB and it means your whole project can be moved anywhere you like.